Electric cable



Patented May 16, 1944 2,348,752 ELEc'rmc CABLE Joshua Creer Quayle,Ashton, Chester, England, assignor to International Standard ElectricCorporation. New York, N. Y.

i Application November 8, 1941, Serial No. 418,406

- In Great Britain September 17, 1940 7 Claims.`

This invention is concerned with cables, in which` a large part of thedielectric surrounding a conductor, particularly that in close proximityto the conductor, is formed of air, the conductor being spaced from itssurroundings by solid material which occupies only a small proportion ofthe intervening space. In particular, it relates to that type of suchcables in which the spacing is effected by a cord or string ofinsulating material wound over the conductor as an open helix. In somecases twoy helices may be arranged c oaxially and may occupy co-axialannular regions one outside the' other. two helices are of differentpitch, or of diierent hand, or of both these diierences.

Such cables are most commonly used for communication purposes and -areemployed where currents of relatively high frequency have to betransmitted, ,such cables being adopted because their construction isconducive either to low dielectric loss or to lowcapacity between theconductor and surrounding conductive bodies,

or for both of these reasons.

It is obviously desirable that in such cables the spacing helices shouldbe of material which has low loss in the circumstances of its use. It isalso desirable that the material should be readily capable of taking upa helical form and retaining this form, that is to say, it should besubstantially self-supporting in the open helical disposition around theconductor when it has been formed into that shape. It has been .foundthat certain natural or artificial thermo-,plastic materials have thedesired properties. On the other hand, a material which isthermo-plastic. while it can readily be placed in position and given thedesired shape, has the tendency to yield under the pressure of theconductor, particularly if the cable is bent and/or if the temperatureshould rise above normal conditions. n such cases the conductor may bedisplaced from4 its intended position and thereby its electricalproperties may be disturbed with corresponding ill eilects on theoperation of the circuit of which it forms part.

The present invention provides an improved form of cable of the kindindicated, in which the helical spacer (or spacers) is formed of neglass bres built up inthe form of cords or tapes and having embodiedtherein, and/or coated thereon, a suitable binding material. Suitablematerials are plastics which have at normal atmospheric temperature asuiiicient rigidity to maintain their position in and on the `groups ofbres and bind the bres together, and which have electric losses v vcounto f itsfilling or coating can readily be' In these latter cases the of alow order when operating under the conditions for which the cable isrequired, particularly at the range of frequency concerned. They arefound in the classes known as thermo-plastic materials, thermo-settingmaterials, and cellulose esters and-ethers; e

By this combination of glass bres and binding material is produced amember which on account of its rigid skeleton of glass fibres will notbe distorted when the cable is bent nor yield under the pressure of theconductor and on acformed, by the aid of heat, if necessary, into anopen helix and will maintain this form subsel quently.

The glass skeleton of the' helical members may be in the form of roving,yarn or string, that is to say, fibres twisted together more or less, orit may consist of fibres laid side by sideA and bonded together solelyby the binding material. 'I'his material must be applied in a liquid, orsemi-liquid, state, which may be arrived at by the aid of a solvent, orby emulsifying, or by softening with the aid of plasticizers and/orheat. 'Examples of suitable materials are polystyrene, polythene that isthenormally solid products of the polymerisation of ethylene-Oppanol(registered trade-mark)that is polymerised isobutylenethermo-settingresins of the Novolak type, cellulose triacetate, and ethyl cellulose.It will be clear that if these are used with plasticisers, or

. any other added materials, .such materials should also have low losscharacteristics. It will be understood that the binder will be appliedto the spacing element before the latter is applied to the conductor.

A conductor with the helical spacing element,

Aor elements, of the kind indicated, may be built up in to a completecable in known manner; for instance, it may be enclosed in an outerconductor forming a substantially complete tube with or Without theinterposition of a tube of dielectric material. Alternatively, two ormore conductors with their spacers can be combined together in a singlecable.

Two forms of construction'of cable, in accordance with` the inventionare shown as examples in the accompanying drawing wherein- Figure l is alongitudinal sectional view of one form;

Figure 2 is a similar view of the'second form of construction;

Figure 3 is an end sectional view of the cable shown in Figure 2; and

Figure 4 illustrates another modification.

In Figure 1 the cable comprises a central wire conductor l around whichis wound an insulating spacing member 2. The latter has the form of anopen helix of relatively long pitch and consists of a string made fromtine glass fibres impregnated with an insulating binding material.Around the spacing member is disposed an insulating tubular member 3example, a glass nbre braided tube or it may be a tube made ofpolythene. The assembly is surrounded by a conducting tubular member Imade of wire braid.

The cable in Figures 2 wireconductors 5, i5

and 3 comprises two provided respectively with spacing members l and 8each having the form of an open helix. The conductor 5 and spacingmember 1 are enclosed in a tubular member 9 and the conductor t andspacing member in a tubular member 9 and I0 are made of glass nbre braidor of polythene, and are enclosed in a tubular member Il which is itselfenclosed in a conducting tubun lar member l2 of wire braid. Thetubularmember Il is of glass fibre braid or of polythene. The completeassembly space cable.

In Figure 1 the conductor I and in Figures f. and 3 the conductors E and5 are surrounded largely by air as the dielectric material.

Fig. 4 illustrates a modification of the construction shown in Fig. lwherein two helices I4 and i5 are arranged coaxially around a centralconductor l so as to occupy coaxial annular' regions, one outside theother.

What is claimed is:

l. An air space electric cable comprising in combination a pair oiconductors, a, spacing member surrounding each conductor in the form ofa cord arranged in an open helix' and comprising a skeleton of glassilbres bonded together with a thermo plastic dielectric binder, a tubeof dielectric material surrounding each said forms a at twin air whichmay be for i it. The tubular members spacing member and a conductingscreen embracing both-said tubes to form a flat twin air space cable. v

2. An air space electric cable as claimed in claim 1 wherein said tubesof dielectric material are composed ofbraided glass libres.

3.An air space electric cable as claimed in .claim 1 wherein said tubesof dielectric material are composed of polythene.

4. An air space electric cable as claimed in claim 1 wherein said tubesof dielectric material are enclosed in a tubular member of dielectricmaterial positioned between said conducting screen and said tubes.

5. .An air space electric cable comprising a conduit, a conductor withinthe conduit and a spacing member between the conductor and the conduit,said spacing member being in the form of a cord of insulating materialcomprising glass bers pre-impregnated and bound together with a thermoplastic dielectric binder, wound in an open helix around the conductorand leaving substantial air space between the conductor and the conduit.

6. An air space electric cable comprising a conduit, a conductor withinthe conduit and al spacing cord wrapped in a loose helix around theconductor between the conduit and the conductor, said spacing cord beingformed of ne glass bers impregnated with an insulating binding material,and being substantially unyielding under pressure.

'7. An air space electric cable comprising a conduit, a conductorconcentrically within the conduit and a spacing cord wrapped in a loosehelix around the conductor between the conductor `and the conduit, saidcord containing a skeleton of iine glass fibers bound by a thermoplasticmaterial and being substantially nondeformable and unyielding.

JOSHUA CREER QUAYLE.

